1. Field of the Invention
The present invention relates to an interface card system which is used to intervene between an SD (Secure Digital) card device and a host system (a CPU system or an SD host system).
2. Description of the Related Art
SD card devices are in widespread use as peripheral devices for extending host system functionality. An SD host controller is a logic circuit incorporated in a host system. The SD host controller exchanges data and commands with an SD host controller on the side of an SD card device via an SD bus interface, thereby controlling the operation of the SD card device.    Patent Document 1: International Publication No. WO 2006/035738
However, data to be exchanged between an SD card device and an SD host controller has often been sent to a host system via a bus on the host system side. This consumes resources such as a CPU, a memory, and the like of a host system and causes an increase in processing load on the host system side.
Also, if a host system includes a host controller capable of controlling two SD card devices independently of each other to transfer data between SD card devices, use of a system which sends data to a CPU on the host system side prior to transfer reduces the throughput.